What are the key features of the sacrum?

There are 5 vertebrae which are fused. There is an ala - lateral. There are 4 anterior sacral foramen (passage for nerves). There is a coccyx on the end. There is the sacral canal, at the bottom there is a sacral hiatus (covered by a membrane - caudal nerve blocks). There is also posterior sacral foramen.

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What is the difference between the True and False Pelvis?

The false pelvis is the part above the pelvic inlet (abdominal cavity). Everything below the pelvic inlet is the true pelvis (pelvic cavity).

What makes up the pelvic inlet?

What is pelvic tilt?

The pelvis is tilted forward 60 degrees anteriorly and the ASIS is line with the pubic symphysis. The sacrum is also titled 40 degrees.

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What are the pelvic boundaries?

Anterior, posterior and lateral walls are all bony. The floor is muscular (pelvic diaphragm).

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Describe male and female variation of pelvis?

In the female the sub-pubic angle is more than 90 degrees whereas in men it is smaller than 90 degrees. In females the inlet is large and circular whereas in men it is heart shaped. The iliac crest are wider in females. The outlet in females is less obstructed - due to childbirth. The sacrum is tilted back in females whereas in males it is tilted forward.

What are the other ligaments in the pelvis?

What are the muscles of the pelvic wall?

1. Piriformis muscle - lateral hip rotators that pass from the body of the sacrum out to the greater trochanter of the hip. 2. Obturator internus muscle - internal in the pelvis and covers majority of the obturator foramen. Lateral rotator.

Describe the venous drainage?

Heaps of venous plexuses all draining to internal iliac veins. The exception is the deep dorsal vein of the penis/clitoris. The rest of perineum drains back with the internal pudendal vein. DDVoP/C passes through anterior deficiency in perineal membrane and then into vesicle/prostatic plexuses.

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Describe the sacral plexus?

L4-S4 - anterior rami. It is joined by L4/5 lumbrosacral trunk. Mostly going on to innervate structures external to pelvis.

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Describe the superior gluteal nerve?

This nerve comes from L4,5 and S1. It supplies the gluteus medius and minimus.

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Describe the inferior gluteal nerve?

This nerve comes from L4, S1,2. It supplies gluteus maximus.

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Where do the gluteal nerves pass?

Superiorly and inferiorly to piriformis muscle respectively.

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Describe the sciatic nerve?

Comes from L4-S3. The tibial nerve always leaves below piriformis whereas the common peroneal may leave below, above or through the piriformis muscle.

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Describe the nerves to Levator Ani and Coccygeus?

These come from S3-4. It innervates the muscular floor, it is at risk during childbirth or extreme pressure to the muscular floor. That is why after childbirth some women are prone to prolapse, because this nerve is damaged.

Sex specific.

Describe the ANS to pelvic viscera?

There are 2 plexuses:1. Superior hypogastric.2. Inferior hypogastric.

What does the superior hypogastric plexus supply?

The anterior body of L5 and sacral promontory.

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What does the inferior hypogastric plexus supply?

Pelvic floor.

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Describe the sympathetic supply of the pelvic viscera?

Comes from L1/2 fibres, they descend into the pelvis via the superior hypogastric plexus and directly from sacral splanchnic nerves. The plexus splits to form two big hypogastric nerves. It causes the contraction of the internal urethral and anal sphincters - continence. It is also involved in ejaculation and moving secretions along epididymis.

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Describe the parasympathetic supply of the pelvic viscera?

Comes from S2-4 fibre, they ascend via hypogastric nerves to superior hypogastric plexus and into abdomen, direct into inferior hypogastric plexus. It causes vasodilation e.g. for erection (male and female). It stimulates the contraction of the bladder.

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What is a saddle fracture?

They involve the pelvic bones, when something has dislocated or fractured the pelvis.